A crankshaft of an internal combustion engine is supported in its journal part by a lower portion of a cylinder block of the engine via a main bearing constituted by a pair of half bearings. In the main bearing, lubrication oil is discharged by an oil pump and fed from an oil gallery in a cylinder block wall, via a through hole in a wall of the main bearing, into a lubrication oil groove formed along an inner surface of the main bearing. Furthermore, the journal part has a first lubrication oil passage passing through the journal part in a diameter direction of the journal part, and openings at both ends of the first lubrication oil passage communicate with the lubrication oil groove of the main bearing. A second lubrication oil passage passing through a crank arm part branches off from the first lubrication oil passage of the journal part, and communicates with a third lubrication oil passage passing through a crankpin in a diameter direction of the crankpin. Thus, the lubrication oil fed from the oil gallery in the cylinder block wall via the through hole into the lubrication oil groove on the inner surface of the main bearing passes through the first lubrication oil passage, the second lubrication oil passage, and the third lubrication oil passage. The lubrication oil is then supplied from a discharge port that opens at an end of the third lubrication oil passage to a gap between the crankpin and a sliding surface of a connecting rod bearing constituted by a pair of half bearings (see JP 08-277831A, for example). The oil is supplied to a gap between a surface of the crankshaft and a sliding surface of the main bearing and the connecting rod bearing.
In order to reduce friction loss during sliding between a crankshaft and a half bearing in such a sliding bearing, it has been proposed to form a plurality of minute recesses on a sliding surface of the half bearing (see JP 58-149622U, JP 2008-95721A, and JP 2000-504089A, for example).